Generally, there have been proposed various lighting apparatuses, and a lighting apparatus comprises a reflector to control a light distribution of a light source, such as a lamp. The reflector is located in a back side of the light source, and reflects light emitted from the light source forward. By the way, a surface of such a reflector is easy to be polluted by indoor-outdoor dirty air. Then, when dirt adheres to the surface of the reflector, the adhesion could cause a decrease in a reflectance of the reflector. In contrast, in the past, there have been proposed a reflector comprising a substrate and a coating layer located on a surface of the substrate.
For example, there have been considered a reflector which comprises a photocatalyst film as the coating layer located on the surface of the substrate. If the photocatalyst film is located as just described, a self-cleaning function can be given to the reflector. That is, if the lighting apparatus is installed in an outdoor location where the surface of the reflector gets wet with rainwater, dirt adhering to the surface of the reflector can be washed away and removed by rainwater. However, when the dirt exceeds the washing capability, the dirt can not be removed from the surface, and furthermore high surface free energy caused by photocatalytic hydrophilicity increases adherence power of the dirt, and rather removal of dirt becomes difficult. Also, the reflector of the lighting apparatus installed indoors rarely gets wet with rainwater directly, and thus the self-cleaning function is not developed and the dirt can not be removed.
On the other hand, the lighting apparatus is often installed in a high place beyond one's reach. Particularly, in late years there has been an increase in the number of the lighting apparatus comprising a long-life light source, and thus maintenance for the lighting apparatus has not been performed regularly. Hence, it is desired that the reflector can maintain a high reflectance for a long term.
Control of surface free energy of the reflector has been considered to solve these problems and demands. Adhesion of dirt is suppressed by controlling the surface free energy. Further, thereby the dirt uniformly adheres to the surface as dots, and can be prevented from spreading widely. As a result, control of the surface free energy can prevent a decrease in the reflectance of the reflector.
Here, an art to control the surface free energy low is disclosed in Japanese Patent Application Laid-Open No. 2000-230060 published on Aug. 22, 2000. A coating layer described in this document is formed of a composition including a macromolecule, which comprises a silicone obtained by copolymerizing a polymerizable silicone containing monomer and a radical polymerizable monomer as a part of combination chain. Also, the art to control the surface free energy low is disclosed in Japanese Patent Application Laid-Open No. 2003-147202 published on May 21, 2003. A coating layer described in this document is formed by sol-gel reaction of a silicon-containing compound and a fluorine-containing compound. Then, these coating layers can realize low surface free energy, and a slipping property of a water droplet can be enhanced.
However, the coating layer in the above No. 2000-230060 is formed of a material of which heat resistance is not so high, and thus there is a problem that the coating layer is not adequate to use for a lighting apparatus of which a light source produces heat. Then, the coating layer in the above No. 2003-147202 is a coating film which is coupled and formed by sol-gel reaction of a water-shedding silane coupling agent, and thus the coating layer has trouble with abrasion resistance and chemical resistance, and there is a problem that the coating layer is not adequate to use for a lighting apparatus.